JPH04125710A - Constant voltage power supply circuit - Google Patents

Abstract

PURPOSE:To turn off the generation of output in the case of a failure to keep a prescribed value by feeding back the output from an input voltage detecting circuit to turn on/off the output voltage and generating the output at the time of rise to a prescribed input voltage. CONSTITUTION:When an input voltage VIN rises to be higher than an output voltage V0 by 5 to 6V, the divided voltage due to resistances R1 and R2 turns on a transistor TR Q3 to absorb the current flowing to a resistance R3, and therefore, a TR Q4 is turned off. The current flowing to a resistance R5 flows to the base of a TR Q1 and the collector of a TR Q2 and flows to the emitter of the TR Q1, and the output is momentarily generated. At this time, the base current of the TR Q3 is increased in comparison with that for turning-on. Meanwhile, when the input voltage is reduced, the base current of the TR Q1 disappears, and the output voltage is not outputted momentarily. Thus, a hysteresis is given to the circuit input voltage to prevent the malfunction.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a constant voltage power supply circuit, and particularly to a constant voltage power supply circuit having a function of inhibiting output at a low input terminal.

[Conventional technology]

As a conventional constant voltage power supply circuit, one having a circuit configuration shown in FIG. 7 is known.

In this circuit, when input voltage v1 is applied, current flows through resistor R4 to Zener tie auto'ZD1,
There is a zener voltage vz on both ends of the zener tie auto ZDI.
occurs, and the base current of transistor Q1 and collector current of transistor Q2 flow through resistor R5, resulting in output voltage V. occurs.

And the output voltage ■. When the voltage increases, the potential at the voltage dividing point formed by resistors R6 and R7 rises, the Hesme current in transistor Q2 increases, and the collector current of transistor Q2 increases, so the base current of transistor Q1 decreases, and as a result, the output Voltage V. decreases.

Conversely, the output voltage V. When the value decreases below the set value, the resistor R6
The divided voltage of R7 decreases, the base current of transistor Q2 decreases, and the collector current also decreases, so the base current of transistor Q1 increases, and as a result, the output voltage V.

Control is performed so that the voltage rises to the set voltage, and it functions as a constant voltage power supply circuit.

[Problem to be solved by the invention]

However, in the conventional example described above, the input voltage VIN of the constant voltage control circuit is equal to the output voltage V. There is a problem in that unless a voltage approximately 3 to 4 ports higher than the set voltage is input, a voltage lower than the set output voltage is output.

Also, when the input voltage VIN gradually increases from zero volts, a voltage approximately 2 to 3 volts lower than the input voltage VIN is output, and conversely, when the input voltage VHH is decreased, the same happens. Output voltage lower than specified occurs.

In recent years, many devices such as microcomputers have been used, and if a power supply having the characteristics shown by the broken line in the input/output voltage characteristic diagram in Figure 6 is used as the power supply for the microcomputer, the output voltage Vo will be lower than that at the input terminal. As VIH rises, it starts up slowly, causing the microcomputer's reset circuit to malfunction, causing the microcomputer to not reset and stop working.Also, when the input voltage decreases, the output voltage V0 also decreases. There was a drawback that the reference voltage of the analog circuit would fluctuate, causing the microcomputer to malfunction.

The present invention has been made to solve the problems of the prior art described above, and aims to provide a constant voltage power supply circuit whose operation is stable and which does not malfunction even when there are fluctuations such as a drop in the input terminal. This is the purpose.

(Means for Solving the Problems) Therefore, the constant voltage power supply circuit according to the present invention is a constant voltage power supply circuit having a configuration in which an output voltage is fed back to an input voltage detection circuit that detects an input voltage value, The above object is achieved by a configuration characterized in that generation of an output voltage is turned on and off based on the output from an input voltage detection circuit, and generation of an output that does not reach a predetermined voltage is prohibited.

[For production]

With the above configuration, the input voltage detection circuit that detects the input voltage value has a configuration in which the output voltage is fed back, and the circuit operation that stabilizes the output voltage is activated by the output from the input voltage detection circuit. Output voltage generation can be turned on and off by the output from the voltage detection circuit, and output is generated when the output voltage rises to the input terminal that can reach the specified value, and when the output voltage cannot be maintained at the specified value. outputs the specified voltage by turning off output generation.

〔Example〕

The constant voltage power supply circuit according to the present invention will be explained below using examples.

FIG. 1 is a circuit diagram of an embodiment according to the present invention.

1 and 2 are input voltage terminals, and 3 and 4 are output terminals. Ql is an output voltage control transistor (hereinafter referred to as transistor Q1), and Q2 is an output voltage detection transistor (hereinafter referred to as transistor Q1).
Q3 is an input voltage detection transistor (hereinafter referred to as transistor Q3), Q4 is an output cutoff transistor (hereinafter referred to as transistor Q4),
R1 and R2 are voltage dividing resistors for detecting input voltage, R
3 is a bias resistor for transistor Q3, R4 is a Zener current limiting resistor, R5 is a bias resistor for transistors Q1 and Q2, R6 and R7 are output voltage setting resistors, and R8 is an output voltage feedback resistor.

Note that an input voltage detection circuit is formed by resistors R1 and R2 and transistor Q3.

In this circuit, the input terminal VIN is applied between input terminals 1 and 2, and when the voltage VIN is gradually increased, the base current flows to the transistor Q4 through the resistor R3, and the current that was about to flow from the resistor R5 to the transistor Q1 is suppressed. Since the transistor Q4 absorbs the voltage, no voltage is generated between the output terminals 3 and 4.

Furthermore, when the input terminal is raised, current flows to the Zener diode ZDI through the resistor R4, and the Zener diode Z
A Zener voltage is generated across DI.

As the input voltage v continues to rise and the input voltage vfN becomes about 5 to 6 volts higher than the output voltage Vo, the resistors R1 and R
The divided voltage by 2 turns transistor Q3 on and absorbs the current flowing through resistor R3, so transistor Q4 turns off, and the current flowing through resistor R5 flows to the base of transistor Q1 and the collector of transistor Q2, and the transistor Current flows to the emitter of Q1 and an output is instantaneously generated.

Also, at this time, since the output voltage Vo is applied to the resistor R8 connected to the output terminal 3, the base current of the transistor Q3 increases compared to when it is in the on state.

Output voltage■. When the input voltage VIN decreases while VO is out, the voltage that turns off the transistor Q3 is determined by the voltage division ratio of the resistors R1 and R2, but the base current flows from the output voltage vo into the transistor Q3 due to the resistor R8. remains on.

Then, when the input voltage VIN is further lowered, the resistor R1
The current of and the current of resistor R8 flow through resistor R2, and the current of resistor R2
However, when the voltage becomes less than V[l- of transistor Q3, it turns off, the base current flows through transistor Q4, the base current of transistor Q1 disappears, and no output voltage is instantaneously output.

As mentioned above, the circuit instantaneously generates an output voltage when the input voltage exceeds a certain level, and bisteresis is applied to the circuit input voltage so that no output voltage is generated when the voltage drops several volts below the input terminal. Therefore, it has the effect of being extremely unlikely to malfunction.

(Other Embodiments) FIG. 2 is a circuit diagram of a second embodiment, in which the same or equivalent parts as in the previous embodiment are denoted by the same reference numerals and redundant explanation will be omitted. In this embodiment, a Zener diode ZD2 is added between the resistors R1 and R2 to the previous embodiment shown in FIG.

In the embodiment shown in FIG. 1, input voltage detection is determined by the voltage division ratio of resistors R1 and R2 and the vBE of transistor Q3, so some variation is unavoidable due to variations in V8E of transistor Q3 and temperature characteristics of VBE. Sometimes it happened. Therefore, in the embodiment shown in FIG. 2, the accuracy of input terminal detection can be improved by adding the Zener diode ZD2. In addition, Zener diode Z
D2 may be inserted in series with the base of transistor Q3.

FIG. 3 is a circuit diagram of a third embodiment. In this embodiment, an operational amplifier is used as a control element to improve human output detection accuracy.
) By using OPI and OF2 in place of the transistors in the previous embodiment, it is possible to provide an accurate output voltage rise point and bisteresis characteristics.

FIG. 4 is a circuit diagram of the fourth embodiment, in which the input terminal V1
When spike-like voltage noise having a pulse with a prominent amplitude is superimposed on N, numerical malfunctions are likely to occur, so the input voltage dividing resistors R1 and R2 of the embodiment shown in FIG. By inserting the capacitor C1 at the dividing point, the operation can be made more stable against power supply noise.

FIG. 5 is a block diagram of a fifth embodiment, in which an output on/off function is provided using a monolithic integrated circuit (IC) voltage regulator ICI. In other words, the input voltage dividing resistors R1 and R2 and the feedback resistor R8 from the output to the input voltage detection terminal generate a specified output voltage when the input voltage reaches a specified value, and when the input voltage drops several volts below the specified voltage, the output voltage is generated. Shutdown operation can be performed.

FIG. 6 is an input/output voltage characteristic diagram of a constant voltage power supply circuit,
In the conventional type, as shown by the broken line, when the input terminal vIN is lower than a certain value, the output voltage V.

The voltage will also be lower than the specified value.

On the other hand, in each embodiment of the present invention, as shown by the solid line in the figure,
When the input terminal reaches a predetermined value V, the output voltage v0 instantaneously generates a specified output voltage, and thereafter maintains a stable output voltage. Then, when the input voltage decreases and reaches an input voltage v2 that cannot maintain the specified output generation voltage, the output voltage instantly becomes zero.

That is, the input terminal detection circuit does not cross the input voltage dividing resistors R1 and R, but outputs the voltage V through the feedback resistor R8. The output from this input terminal detection circuit turns the output voltage generation on and off, prohibiting output below the specified voltage, and providing a stable output voltage while output is being generated. Something will happen.

〔Effect of the invention〕

As described above, according to the present invention, the input voltage detection circuit that detects the input voltage value has a configuration in which the output voltage is fed back, and the circuit operates to stabilize the output voltage by the output from the input voltage detection circuit. is activated, and output voltage generation can be turned on and off by the output from this input voltage detection circuit, and when the output voltage rises to the input voltage that can reach the specified value, an output is generated, and the output voltage reaches the specified value. Since output generation is turned off when the value cannot be maintained, it is possible to output a stable specified voltage and provide a constant voltage power supply circuit that can prevent connected equipment from malfunctioning.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram of the first embodiment of this invention, Fig. 2 is a circuit diagram of the second embodiment, Fig. 3 is a circuit diagram of the third embodiment, and Fig. 4 is a circuit diagram of the fourth embodiment. , FIG. 5 is a block diagram of the fifth embodiment, FIG. 6 is an input/output voltage characteristic diagram, and FIG. 7 is a conventional constant voltage power supply circuit diagram. R1, R2...Input voltage detection resistor R3-R5-
--- Bias resistor R6, R7... Output voltage detection resistor Q 1 ---
---Power control transistor Q 2-...Control transistor

Claims (1)

[Claims] A constant voltage power supply circuit having a configuration in which an output voltage is fed back to an input voltage detection circuit that detects an input voltage value, and the output voltage is turned on and off based on the output from the input voltage detection circuit to reach a predetermined voltage. A constant voltage power supply circuit characterized in that generation of an output that does not occur is prohibited.